1. Field of the Invention
The present invention relates to a structure of a semiconductor device including a plurality of protruding external electrodes such as a solder ball or solder bump arranged on a main surface and a test terminal, and a structure of an IC socket used for testing a semiconductor device.
2. Description of the Background Art
Conventional semiconductor devices such as the BGA (Ball Grid Array) type, CSP (Chip Scale Package) type, and KGD (Known Good Die) type having a plurality of protruding external electrodes arranged on a main surface are known. An example of such a BGA type semiconductor device is shown in FIG. 11. Referring to FIG. 11, a BGA semiconductor device 1 includes a mold resin 2, a LSI chip 3, a wire 4, an adhesive 5, an interconnection layer 6, a substrate 7, an internal conductor 9, and a solder ball 10.
LSI chip 3 is mounted at the backside of substrate 7 and covered with mold resin 2. LSI chip 3 is connected to interconnection layer 6 via wire 4. A through hole 8 is formed in substrate 7. Internal conductor 9 is formed in through hole 8. Solder ball 10 is formed on internal conductor 9.
FIG. 12 is a plan view of the BGA type semiconductor device of FIG. 11. The sectional view taken along line XI--XI of this FIG. 12 is shown in FIG. 11. It is appreciated that solder balls 10 are arranged in a matrix at the main surface of substrate 7, as shown in FIG. 12. In the present specification, the surface where a protruding electrode such as solder ball 10 is arranged is called the main surface of the semiconductor device.
An IC socket as shown in FIG. 13 can be used in testing a BGA type semiconductor device 1 of the above-described structure. This IC socket includes a body 12, an alignment plate 14, a spring 15, and a contact pin 13. Alignment plate 14 is supported by spring 15, and includes a through hole for receiving solder ball 10 and contact pin 13. Contact pin 13 abuts against the bottom of solder ball 10 in the through hole. Testing was carried out by bringing contact pin 13 of the IC socket directly in contact with solder ball 10.
This direct contact between contact pin 13 and the bottom of solder ball 10 sometimes causes deformation of solder ball 10, whereby adjacent balls 10 are short-circuited to each other after mounting.
The surface of a solder ball 10 is formed mainly of a curve as shown in FIG. 13, and has convex and concave portions in many cases. When contact pin 13 is brought directly in contact with such a solder ball 10, contact pin 13 may form contact only with the convex portion at the surface of solder ball 10. In this case, the area of contact between contact pin 13 and solder ball 10 is reduced. There is a problem that appropriate electrical characteristics cannot be obtained during testing.
There is also a possibility that solder scraps may be adhered to the tip of contact pin 13 when direct contact is provided between solder ball 10 and contact pin 13. In this case, contact failure between contact pin 13 and solder ball 10 may occur due to oxidation of the solder scraps attached at the tip of contact pin 13. There is also a possibility of the solder scraps at contact pin 13 being transferred to another solder ball 10 to cause shorting between solder balls 10 after mounting.